Lexiconメーカー20/20 ADの使用説明書/サービス説明書
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20/20 AD 20 Bit A/D Converter User Guide.
Lexicon Copyright © 1992 Lexicon Inc. 3 Oak Park Bedford, MA 01730 Tel: 781-280-0300 Fax: 781-280-0499 All Rights Reserved This publication is protected by copyright and all rights are reserved. No part of it may be reproduced or transmitted by any means or in any form, without express prior consent in writing from Lexicon.
20/20 AD User Guide SAFETY SUMMARY The following general safety precautions must be observed during all phases of operation, service and repair of this instrument. Failure to comply with these precautions, or with specific warnings elsewhere in these instructions violates safety standards of design manufacture and intended use of the instrument.
20/20 AD User Guide Contents Introduction Controls and Connectors ...................................................................... 1 Unpacking • Power • Mounting .......................................................... 1 Front Panel Controls .
20/20 AD User Guide Introduction The 20/20 AD is an analog-to-digital converter which can be configured for two 20-bit channels, or four 18-bit channels. Twin on-board signal processors provide 20-bit to 16-bit compression in the digital domain, as well as DC removal and a choice of four dither types.
1 Controls and Connectors 20/20 AD User Guide After unpacking the 20/20 AD, save all packing materials in case you ever need to ship the unit. Thoroughly inspect the 20/20 AD and packing materials for signs of damage. Report any shipment damage to the carrier at once.
Lexicon 2 Controls and Connectors 1dB SCALE ALT PK HOLD ATTEN 1 THRESH UNBAL THRESH UNBAL 2 3 THRESH UNBAL THRESH UNBAL 4 4 CHAN ~ EMPH OVL 0 3 6 12 18 24 30 36 42 60 OVL 0 3 6 12 18 24 30 36 42 60 MU.
3 Controls and Connectors 20/20 AD User Guide The Level Meters When the compressor is off , the behavior of the level meters is determined by the settings of the 1dB SCALE, and PK HOLD switches.
Lexicon 4 Controls and Connectors AES/WC In internal sync mode, PRES indicates that either WC or AES is available at the inputs as a sync source. In external sync mode, PRES indicates that the selected sync source is present at the input connectors. Synchronization and Output Formatting SAMPLE RATE Selects the sample rate of the A/D conversion.
5 Controls and Connectors 20/20 AD User Guide PUSH DO WORD CLOCK IN DO 3 + 4 1 + 2 OUT AES SYNC IN V ~ PUSH 4I N 3 UNBAL BAL PUSH PUSH 2I N 1 UNBAL BAL PUSH Digital Output Two 3-pin XLR connectors, professional format AES bal- anced digital outputs. Two consumer format optical (fiber-optic) outputs.
Lexicon 6 Controls and Connectors Audio Connections XLR Pinout Signal Mating Connector Description AES/EBU XLR A3M Balanced RS-422 Digital Input AES/EBU XLR A3F Balanced RS-422 Digital Output S/PDIF R.
7 Controls and Connectors 20/20 AD User Guide AES/EBU Digital Output This interface requires balanced connections using high-quality, low-capaci- tance, controlled-impedance, data communication, twisted-shielded pair cable. Microphone cable may introduce a significant amount of jitter into the signal, causing distortion.
9 Using the 20/20 AD 20/20 AD User Guide Analog Inputs The 20/20 AD has four analog inputs: CH1, CH2, CH3 and CH4. In two-channel mode, only CH1 and CH2 are used, and the dynamic range of the unit is extended.
Lexicon 10 Using the 20/20 AD Jumper settings (as set at the factory) W18 CHASSIS GROUND ANALOG IN AES SYNC IN WORD CLOCK IN AES OUT S/PDIF OUT XLR CONNECTOR SHIELDED TWISTED PAIR BNC CONNECTOR 75 OHM.
11 Using the 20/20 AD 20/20 AD User Guide The following figure indicates the locations and factory settings of these jumpers on the board. In their closed positions, the jumpers have their right two (or lower two) pins shunted together. To open a jumper, move the shunting block to the left (or upper) two pins.
Lexicon 12 Using the 20/20 AD Make sure the BALANCE switches located on the rear panel are set to match the type of input. (OUT=balanced , IN=unbalanced). The red UNBAL lights on the front panel will indicate an error if there is a mismatch between the switch setting and the signal type.
13 Using the 20/20 AD 20/20 AD User Guide Adjust the front panel Gain knobs until the peak input levels are balanced and come within a few dB of clipping.
Lexicon 14 Using the 20/20 AD The 20/20 AD can synchronize to its internally derived sample clock at 44.1kHz or 48kHz, or to an external AES or Word Clock signal, in the range of 41-51kHz. The EXT SYNC switch allows you to select external Word Clock (WC), external AES (AES), or internal source (WC and AES off).
15 Using the 20/20 AD 20/20 AD User Guide The 20/20 AD is shipped configured for Internal mode. To operate in External mode, press EXT SYNC until the desired sync source (WC or AES) lights. If the selected sync source light flashes and the PRES light is not on, it indicates that there is no signal present as a sync source.
Lexicon 16 Using the 20/20 AD About Dither Dither is a low-level pseudo-random signal which is added to digital audio to reduce quantization noise, in effect, by replacing it with a “ nicer sounding ” noise.
17 Using the 20/20 AD 20/20 AD User Guide -160.0 -150.0 -140.0 -130.0 -120.0 -110.0 -100.0 -90.00 -80.00 -70.00 -60.00 0.0 2.00k 4.00k 6.00k 8.00k 10.0k 12.0k 14.0k 16.0k 18.0k 20.0k Plot of noise + distortion vs. frequency for the 20/20 AD in 2- channel mode with a -60dBfs sinewave at 1kHz.
Lexicon 18 Using the 20/20 AD Automatic Offset Removal DC offsets are created by input amplifiers and A/D converters for a number of reasons. In the 20/20 AD, these typically include temperature changes, changes between 2-channel and 4-channel mode, change of sample rate or sync source, or large adjustments of input level controls.
19 Using the 20/20 AD 20/20 AD User Guide ___| threshold |___ | threshold| – gain ratio = Note that the 6dB GAIN setting is given only as an example.
Lexicon 20 Using the 20/20 AD 0dB -3dB -6dB -8dB -10dB -12dB -14dB -16dB -18dB -20dB -22dB -24dB -26dB -30dB -36dB 1 1.50:1 1.20:1 1.14:1 1.11:1 1.09:1 1.07:1 1.06:1 1.06:1 1.05:1 1.05:1 1.04:1 1.04:1 1.03:1 1.02:1 2 3.00:1 1.50:1 1.33:1 1.25:1 1.20:1 1.
21 Using the 20/20 AD 20/20 AD User Guide When RELEASE is set to 0, the compressor acts like an amplifier with a non- linear transfer function. For example, setting GAIN to 6dB and THRESHOLD to -14dB produces a close approximation of a generic tape saturation curve.
Lexicon 22 Using the 20/20 AD To summarize: 1. Set the input levels so that the peak level is a few dB below clipping. 2. Turn on the compressor. 3. Set compressor GAIN to the input level safety margin, and THRESHOLD to 0dB. 4. Adjust RELEASE to suit the program material.
23 Using the 20/20 AD 20/20 AD User Guide In 2-channel mode, when the LINK switch is off, each of the two channels is compressed independently. When the LINK switch is on, the louder of the two channels sets the amount of compression. This serves the same function as “ stereo link ” in analog compressors.
Lexicon 24 Using the 20/20 AD When recording in 4-channel mode to two DAT recorders, it may be useful to record a "clapper" signal to both DATs to facilitate realignment during post- production.
Definition of Terms 26 20/20 AD User Guide Definition of Terms AES : Audio Engineering Society. aliasing : a form of distortion which occurs when an A/D converter’s sample rate is less than twice the highest fre- quency component of a signal. amplitude : the maximum departure of the value of a wave- form from its average value.
Definition of Terms 27 20/20 AD User Guide Definition of Terms AES : Audio Engineering Society. aliasing : a form of distortion which occurs when an A/D converter’s sample rate is less than twice the highest fre- quency component of a signal. amplitude : the maximum departure of the value of a wave- form from its average value.
3 Oak Park Bedford, MA 01730 USA Tel: 781-280-0300 Fax: 781-280-0499.
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